This invention relates to metal organic compounds, compositions containing them, and their use.
Compounds comprising three atoms of a divalent metal e.g. cobalt, each linked through oxygen atoms to a boron or phosphorus atom and comprising aliphatic monocarboxylic acid residues bonded to the metal are known. Such known compounds have been used as additives to rubber skim stock to improve adhesion of the rubber to metal.
They are provided in a form which is readily handleable, and in particular is not inherently tacky or viscous.
The present invention provides new compounds which have the advantages of the aforesaid known compounds but which improve still further the adhesion of rubber to brass coated steel cord and the retention of such adhesion under conditions of steam and salt ageing, when compared to the known cobalt-containing compounds.
According to the present invention there are provided metal-organic compounds for use in promoting adhesion of rubber to metal, of average formula:
X(OMAxe2x80x2p)m(OMBxe2x80x2q)n
in which:
X is Aluminium (Al,), Titanium (Ti,), Zirconium (Zr,), alkyl or aryl silicon (Rxe2x80x94Si), di-alkyl, di-aryl or alkyl, aryl silicon (Rxe2x80x3Rxe2x80x2xe2x80x2Si) or silicon (Si);
M is cobalt or nickel, preferably cobalt (II);
Axe2x80x2 is an aliphatic carboxylic acid residue (of general formula R1COO) of 7 to 15 carbon atoms;
Bxe2x80x2 is an aromatic carboxylic acid residue (of general formula RCOO) of 7 to 15 carbon atoms; or an aryloxy substituted aliphatic or aromatic carboxylic acid of 8 to 15 carbon atoms;
p and q are, independently 0.5 to 1.5, preferably 1.0; m+n=x, wherein x is the valency of X, m/n is typically from 0.67 to 9.0, preferably from 1.5 to 4.0;
typically n is 0.2 to (xxe2x88x921), preferably 0.5 to 3, and especially 0.5 to 1.4.
When X is alkyl- and/or aryl-substituted silicon, the alkyl group is preferably one having 1 to 4 carbon atoms, especially methyl, while the aryl group is preferably phenyl. Typical examples include methylsilicon, dimethylsilicon, diphenylsilicon and methyl, phenylsilicon.
The aliphatic carboxylic acid (Axe2x80x2H) is preferably a monocarboxylic acid, e.g. n-heptanoic acid, 2,2-dimethylpentanoic acid, 2-ethylpentanoic acid, 4,4-dimethylpentanoic acid, n-octanoic acid, 2,2-dimethylhexanoic acid, 2-ethylhexanoic acid, 4,4-dimethylhexanoic acid, 2,4,4-trimethylpentanoic acid, n-nonanoic acid, 2,2-dimethylheptanoic acid, 6,6-dimethylheptanoic acid, 3,5,5-trimethylhexanoic acid, n-decanoic acid, 2,2-dimethyloctanoic acid, 7,7-dimethyloctanoic acid, n-undecanoic acid, isoundecanoic acid, cekanoic or the mixture of 2,2,2-trialkyl acetic acids known as neodecanoic acid.
The aromatic carboxylic acid (Bxe2x80x2xe2x80x94H) may be, for example, benzoic acid, an alkyl-, alkoxy-, amino-, halogen-, thio-, or hydroxy-substituted benzoic acid, such as 2-, 3-, or 4-methylbenzoic acid, salicylic acid, 3,5-diisopropyl salicylic acid, 3,5-di-tertbutyl salicylic acid, anthranilic acid, or 4-chloro-benzoic acid, phthalic acid, terephthalic acid, cinnamic acid, or a more complex aromatic acid comprising a conjugated ring system. When Bxe2x80x2xe2x80x94H is an aryloxy substituted acid it is preferably a phenoxysubstituted aliphatic or aromatic acid, especially phenoxyacetic acid and phenoxypropionic acid.
The metal organic compound may be associated with a borate of an element of group IA or IIA of the Periodic Table (ie. an alkali metal or an alkaline earth metal). Said borates may be present at a concentration of up to, say, 20% by weight of the metal compound. Suitable borates include sodium borate, potassium borate, calcium borate and magnesium borate.
The metal organic compound may also be associated with microcrystalline wax and/or process oil, and/or a hydrocarbon resin and/or a resorcinol/formaldehyde resin.
The novel metal organic compounds may be incorporated as adhesion promoters in rubber skim stock comprising rubber and conventional rubber compounding ingredients. The metal organic compound is typically present in an amount from 0.2 to 2 parts by weight per hundred parts by weight of rubber, and preferably the metal organic compound provides about 0.224 parts by weight of cobalt metal per hundred parts by weight of rubber.
The metal organic compounds of the present invention may be made by heating together a mixture in the required proportions of (1) the acids Axe2x80x2H and Bxe2x80x2H which give rise to the residues Axe2x80x2 and Bxe2x80x2 as defined above, (2) a source of cobalt or nickel such as the oxide, hydroxide or carbonate, (3) an aluminate, silicate or titanate ester of a lower alcohol, e.g. n-butanol, and (4) an acid capable of forming a volatile ester with the lower alcohol residues present in the said ester, e.g. acetic acid or propionic acid, and distilling off the said volatile ester, preferably under reduced pressure. All of the acids (1) and (4) and the metal source (2) must be pre-reacted before the ester (3) is added. The reaction temperature is typically in the range 50 to 250xc2x0 C.